Officials in India are launching a campaign to cheer the flagging spirits of listless river dolphins amid fears that toxic pollution has left them miserable.

They are planning to use the popularity of the freshwater dolphins to revive the Ganges, the country's holiest river, and reduce chemical pollution in its waters.

The number of dolphins in India has more than halved from 5000 in 1982 to just 2000 today. Up to 160 die every year because of fishing and pollution.

The Ganges is one of India's most polluted rivers and has become an open sewer, burial ground and chemical dump in several stretches.

Conservationists said the health and happiness of its dolphins is a key indicator of the level of pollution in its waters.

"The Ganges dolphin is a solitary animal compared to to marine dolphins but occasionally we see these dolphins engage in fun and joy in their habitat," said Professor R K Sinha, who has studied the Ganges Dolphin for more than 30 years. More recently however, as river pollution has increased, they have not displayed their customary joy.